/Engine/Source/Runtime/GeometryCore/Public/Util/IndexUtil.h
Find ordered edge [VertexID1,VertexID2] in a triangle that is in an array of triangles, and return remaining third vertex
vertex id of other vertex, or InvalidID if not found
namespace IndexUtil { int IndexUtil::FindTriOtherVtx ( int VertexID1, int VertexID2, const [TDynamicVector](API\Runtime\GeometryCore\Util\TDynamicVector)< [FIndex3i](API\Runtime\GeometryCore\FIndex3i) > & TriIndexArray, int TriangleIndex ) }